Consecutive Annealing Research Articles

Outstanding Activity and Durability of Supported NiCo2O4 Nanoparticles for Direct Ethanol Fuel Cells

ABSTRACTThe rational design of noble metal‐free electrocatalysts represents one of the basic stones for fuel cell development. With the exploration of eco‐friendly nanomaterials for the investigated alcohol oxidation process, nickel‐based electrodes have been recognized as the most auspicious anodes with promoted activity and stability. In this work, a series of NiCo2O4 nanoparticles were deposited onto graphite sheets (NiCo2O4/T) introducing varied proportions of cobalt oxide species. Co‐precipitation protocol of the respective metallic hydroxides onto the carbonaceous support was followed with consecutive annealing in an air atmosphere at 400°C. The fabricated mixed metallic oxide nanopowder was physically studied using X‐ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive X‐ray analysis (EDX), X‐ray photoelectron spectroscopy (XPS), and selected area electron diffraction (SAED). Uniformly arranged nanoparticles were observed on graphite surface as evidenced by SEM and TEM. The cubic lattice structure of formed NiCo2O4 crystals was also confirmed by XRD through the defined peaks of binary metallic oxides clarifying their successful preparation scheme. The electrocatalytic properties of these NiCo2O4/T nanocatalysts were evaluated for oxidizing ethanol molecules in basic solution. Pronounced oxidation current densities were remarkably measured at NiCo2O4/T electrodes in relation to that at NiO/T. Differing the introduced cobalt oxide content into the synthesized nanocatalyst significantly controlled its catalytic performance. NiCo2O4/T‐20 exhibited the highest activity and stability among the prepared nanomaterials. Much decreased charge transfer resistances were also recorded at this electrode demonstrating its promoted electron transfer characteristics. This work could provide a reasonable route for the simple synthesis of comparable transition metallic oxides with promising attitudes for energy generation purposes.

Plasma processing and annealing for defect management at SiO2/Si interface

The defect generation and recovery at the SiO2/Si interface are studied in argon (Ar) plasma irradiation and consecutive annealing. The defects are generated by the Ar plasma irradiation and recovered by annealing. The recovery of defects strongly depends on the origins of defect generation, i.e., photon irradiation or ion bombardment. The photon-induced defects are nearly fully recovered by annealing at 300 °C, whereas the ion-induced defects are not sufficiently recovered. With high-energy bombardments of ions at ⪆200 eV, the residual defects are created at the 5 nm-thick thermal-SiO2/Si interface. The ion energy should be properly controlled in plasma processing for high-performance device fabrication.

Large-area homoporous membranes (HOMEs) enabled by multiple annealing

Homoporous membranes (HOMEs) featuring through pores with almost identical apertures, are highly desired for high-precision separations. It remains a major challenge to produce large-area HOMEs because the microstructure control and defect annihilation become increasingly difficult when membrane sizes are dramatically increased. Herein, we propose a multiple annealing strategy to fabricate large-area HOMEs. Polystyrene-block-poly(2-vinyl pyridine) (PS-b-P2VP) films are first coated on smooth and large substrates. Being annealed by chloroform vapor, perpendicularly aligned P2VP cylinders are formed within the films, and further converted into through pores via the mechanism of selective swelling-induced pore generation. It is shown that the conventional single-time annealing is inadequate to create the ordered through pores, because P2VP chains may have no sufficient time to locomote to the right position as required for the ideal hexagonally arranged ordering. By virtue of the multiple annealing, well-defined through pores can be generated after consecutive annealing for three times, as more P2VP chains aggregate into the ideally ordering position. The films are transferred and composited onto macroporous substrates, producing composite membranes with an effective area of up to ∼100 cm2. The resultant membranes exhibit excellent separation performances. Importantly, HOMEs can be fabricated on low-cost substrates via this strategy, highlighting their great promise in real-world applications of high-precision separations.

Sol-gel-based metal-oxide thin-film transistors for high-performance flexible NMOS inverters

High-performance metal-oxide thin-film transistors (oxide-TFTs) with high-k zirconium dioxide (ZrO2) dielectric and indium-gallium-zinc oxide (IGZO) semiconducting films were developed on flexible polyimide substrates. The flexible IGZO-TFTs fabricated using a simple and effective sol-gel-based solution-process combined with oxygen-enriched consecutive annealing at 200 °C, exhibited a high field-effect mobility of 13.6 cm2 V−1 s−1 at 5 V, on/off ratio of 1.05 × 106, gate leakage current of 2.7 × 10−11 A, and threshold voltage of 0.44 V. The effects of O2 annealing on the film quality of the sol-gel-based ZrO2 and IGZO were investigated by analyzing the crystallinity, morphology, and degree of metal-oxygen bonding states. Temperature-dependent steady-state direct-current measurements over the temperature range of 90–300 K, and time-domain non-quasi-static transient measurements with a minimized resistance-capacitance time constant were performed. Thus, the activation energy, density of states, interface trap density, and velocity distribution were determined to investigate the charge transport mechanism responsible for the high performance of the oxide- TFTs proposed in this study. An enhancement-load-type N-channel metal-oxide semiconductor (NMOS) inverter consisting of two oxide-TFTs fabricated via O2 annealing was demonstrated. The flexible NMOS inverter exhibited a high gain of 10.8 at 5 V and outstanding mechanical stability against 10,000 cycles of bending stresses at a strain of 30% without a passivation or buffer film.

Extraordinary simultaneous enhancement of the coercivity and remanence of dual alloy HRE‐free Nd‐Fe‐B sintered magnets by post‐sinter annealing

• Both the remanence and coercivity are improved after the 2nd annealing process. • The coercivity is hugely increased from 10.09 kOe for the as-sintered sample to 17.19 kOe for the 2nd annealed magnet, with a significant increment of 70.37%. • The matrix grains are enveloped by a (Pr,Nd,Cu,Ga)-enriched layer after the 2nd annealing process. • HRE-free Nd-Fe-B sintered magnets with excellent comprehensive magnetic properties were manufactured by Pr-Fe-Ga boundary addition. Post-sinter annealing process plays an important role in the microstructures and magnetic properties of the Nd-Fe-B sintered magnets. In this paper, systematically investigated are the magnetic properties and microstructures of the as-sintered and post-sinter annealed Nd-Fe-B magnets with Pr-Fe-Ga boundary addition. Two choice consecutive annealing methods are adopted at high and low temperatures, namely the 1 st annealing at 880 ºC for 2 h and then the 2 nd annealing at 440 ºC for 3 h. It is exceptional to find out that both the remanence and coercivity are improved after 2 nd annealing process for this type of magnet. The coercivity is hugely increased from 10.09 kOe for the as-sintered sample to 17.19 kOe for the 2 nd annealed magnet, with a significant increment of 70.37% in coercivity. The extraordinary magnetic properties of B r =14.44 kGs, H cj =17.19 kOe and ( BH ) max =51.08 MGOe are obtained for the designated Nd-Fe-B sintered magnets without heavy rare earth (HRE) elements manufactured by dual alloy method. The Curie temperature is monotonically decreased from 634 K to 602 K while the c -axis alignment degree is optimized after annealing. Microstructural observation and analysis indicate that the elemental distribution patterns are altered after the 2 nd annealing. The diffusion of the aggregate (Pr,Nd,Cu,Ga)-rich phase from triple junctions into the grain boundary regions is ascribed to the formation of thin and continuous grain boundary layer, which is critical to improve the microstructures and magnetic properties.

Hierarchically structured MoO2/dopamine-derived carbon spheres as intercalation electrodes for lithium-ion batteries

A hydrogen peroxide initiated sol-gel process involving molybdenum transformation in the presence of dopamine (Dopa) hydrochloride excess produced the metastable precipitate composed of polydopamine (PDopa) spheres coated with Dopa preintercalated molybdenum oxide, (Dopa)xMoOy@PDopa. The hydrothermal treatment (HT) of the (Dopa)xMoOy@PDopa precursor resulted in the simultaneous carbonization of Dopa and molybdenum reduction generating MoO2 nanoplatelets distributed and confined on the surface of the Dopa-derived carbon matrix (HT-MoO2/C). The consecutive annealing (An) of the HT-MoO2/C sample at 600 °C under Ar atmosphere led to the formation of MoO2 with increased Mo oxidation state and improved structural stability (AnHT-MoO2/C). Annealing had also further facilitated interaction between the molybdenum-derived and Dopa-derived components resulting in the modification of the carbon matrix confirmed by Raman spectroscopy. Morphology of both materials is best described as Dopa-derived carbon spheres decorated with MoO2 nanoplatelets. These integrated metal oxide and carbon structures were tested as electrodes for lithium-ion batteries in the potential window that corresponds to the intercalation mechanism of charge storage. The AnHT-MoO2/C electrode showed enhanced electrochemical activity, with an initial specific discharge capacity of 260 mAh/g and capacity retention of 67% after 50 cycles, compared to the HT-MoO2/C electrode which exhibited an initial specific discharge capacity of 235 mAh g−1 and capacity retention of 47% after 50 cycles. The rate capability experiments revealed that the capacity of 93 mAh/g and 120 mAh/g was delivered by the HT-MoO2/C and AnHT-MoO2/C electrodes, respectively, when the current density was increased to 100 mA/g. The improved specific capacity, electrochemical stability, and rate capability achieved after annealing were attributed to higher crystallinity of MoO2, increased oxidation state of Mo, and formation of the tighter MoO2/carbon contact accompanied by the annealing assisted interaction between MoO2 and Dopa-derived carbon.

Annealing of Silicon Heterojunction Solar Cells: Interplay of Solar Cell and Indium Tin Oxide Properties

In this paper, we report the evolution of silicon heterojunction solar cell properties focusing, in particular, on the indium tin oxide (ITO) layers upon consecutive thermal annealing. We find that the charge carrier density N <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">e</sub> of the ITO increases with higher thermal budget, while the carrier mobility remains constant. For the solar cells, their series resistance at the maximum power point R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MPP</sup> first decreases due to the reduction of the ITO's sheet resistance. With further annealing, R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MPP</sup> increases again. As all monitored R <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">S</sub> components decrease, we attribute this to an increase of the contact resistance. The implied V <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">OC</sub> and the implied fill factor both slightly degrade for annealing temperatures above 190 °C for our layers. This, as well as the change in Ne of the ITO, must be carefully considered when optimizing the thermal budget needed, e.g., for sputter damage or screen-printing paste curing.

Oligomer‐Incorporated Polymeric Layer Framework of Graphitic Carbon Nitride for Effective Photocatalytic Hydrogen Evolution

AbstractThis paper presents a structural design of graphitic carbon nitride (CN) for use as an active photocatalyst in H2 evolution reactions. The active photocatalyst is synthesized by subjecting a CN sample to consecutive annealing and ammonia treatments. The CN sample is produced through urea condensation. The annealing treatment destroys the polymeric CN to form a defective polymeric layer framework incorporating 1,3,4,6,7,9,9b‐Heptaazaphenalene‐2,5,8‐triamine (melem) oligomers. The annealed CN exhibits a wide absorption range in visible light because the distorted structure causes conjugation of the π‐orbital with a nitrogen nonbonding state. The subsequent ammonia treatment of the annealed CN repairs the nitrogen vacancies and bridges the polymeric framework and melem oligomers. The repaired and bridged sample (N‐aCN) provides viable pathways for charge separation and transport, and active amino sites are introduced in the sample for electron injection in order to produce H2. When Pt is deposited, the CN and N‐aCN samples catalyze H2 evolution from aqueous triethanolamine solution at quantum yields of 3.7 and 17%, respectively, under 420 nm monochromatic irradiation. The high activity of N‐aCN demonstrates that the oligomer‐incorporated polymeric layer framework effectively harvests light and mediates charge transport in CN materials for photoenergy conversion.

From zinc-cyanide hybrid coordination polymers to hierarchical yolk-shell structures for high-performance and ultra-stable lithium-ion batteries

Uniform zinc-cyanide hybrid coordination polymer microspheres were successfully synthesized by a coprecipitation method. Then hierarchical yolk-shell structured and carbon coated ZnO microspheres (YC-ZnO) composed of ZnO@C nanocrystals were prepared by consecutive post annealing processes of these microspheres in argon and air atmosphere. Such micro-nano porous structures have the advantages of large specific surface area, good charge transport kinetics, and large cavity to accommodate the volume change and maintain the mechanical integrity of the electrode material. When evaluated as anode materials of lithium ion batteries, these ZnO yolk-shell spheres exhibited excellent battery performance with a high rate capacity and ultra-stable cycling stability.

Stopping cross sections of protons in Ti, TiO2 and Si using medium energy ion scattering

Stopping cross sections of protons in Ti, Si, and TiO2 films in the energy range 50–170 keV were determined from medium energy ion scattering (MEIS) spectra by an iterative procedure. The energy loss of protons was investigated for pure Ti and Si films, deposited by molecular beam epitaxy (MBE) onto n-Si(100) and diamond-like carbon (DLC) substrates respectively. Consecutive annealing of Ti at 200 °C in O2 resulted in stoichiometric TiO2 thin-films. Thickness and composition of the films and the interfacial properties were determined using Rutherford backscattering spectroscopy (RBS), MEIS, and X-ray photoelectron spectroscopy (XPS). Calculated stopping cross sections of Ti, Si, and TiO2 in the range of energies were compared with the commonly used SRIM2003 values. For Ti and Si, SRIM2003 values appear to be overestimated over the entire energy range. The new stopping cross sections explain deviations from previously reported values for SrTiO3. We note that the stopping cross sections of O in a gaseous phase, used in Bragg’s rule calculations, cannot be applied for accurate quantitative ion beam analysis in solid compounds in the medium ion energy range.

Temperature Dependence of the Magnetization of the Ni52Mn24Ga24 Alloy in Various Structural States

are presented of a study of the temperature dependence of the magnetization σ(Т) of the polycrystalline Ni52Mn24Ga24 alloy in various structural states: in the initial coarse-grained state, after severe plastic deformation by high pressure torsion, and after stepped annealing of the deformed specimen at temperatures from 200 to 700°С for 30 min. As a study of the σ(Т) curve shows, in an alloy possessing a coarse-grained initial structure, a martensitic phase transition and a magnetic phase transition are observed in the room temperature interval. The martensitic transformation takes place in the ferromagnetic state of the alloy. This transformation is accompanied by an abrupt lowering of the magnetization of the material, associated with a lowering of the symmetry of the crystalline lattice and a high value of the magnetocrystalline anisotropy constant of the alloy in the martensitic phase. It is shown that as a result of plastic deformation there takes place a destruction of ferromagnetic order and a suppression of the martensitic transformation. Consecutive annealing after deformation leads to a gradual recovery of ferromagnetic order and growth of the magnetization of the material. Recovery of the martensitic transformation begins to be manifested only after annealing of the alloy at a temperature of 500°С, when the mean grain size in the recrystallized structure reaches a value around 1 μm.

Development of a new ultrafine grained dual phase steel and examination of the effect of grain size on tensile deformation behavior

Ultrafine grained dual phase (DP) steels are among the newest grades of DP steels that incorporate the uniform distribution of fine martensite particles (in the order of 1–2μm) within a ferrite matrix. These new grades of steels have been developed in response to the world׳s demand for decreasing the fuel consumption in automobiles by increasing the strength to weight ratio. In the present research, a new kind of ultrafine grained DP (UFG-DP) steel with an average grain size of about 2μm as well as a coarse grained DP (CG-DP) steel with an average grain size of about 5.4μm was produced by consecutive intercritical annealing and cold rolling of low carbon AISI 8620 steel. The martensite volume fraction for both microstructures was the same and about 50 percent. Scanning electron microscopy (SEM) microstructural examination and room temperature tensile deformation analyses were performed on both UFG-DP and CG-DP steels and their deformation behavior in terms of strength, elongation and strain hardening was studied and compared. Room-temperature uniaxial tensile tests revealed that for a given martensite volume fraction, yield and tensile strengths were not very sensitive to martensite morphology. However, uniform and total elongation values were noticeably affected by refining martensite particles. The higher plasticity of fine martensite particles as well as the more uniform strain distribution within the UFG-DP microstructure resulted in higher strain hardenability and, finally, the higher ductility of the UFG-DP steel.

Refraction in plane-parallel plate—Reconsideration of method of measurement of refractive indices

The prism (minimum deviation) method of measurement of refractive indices in solids has a couple of disadvantages including problems associated with manufacturing of a good prism itself. Besides this method is unsuitable to be used in piezo- and electro-optical experiments when one needs to achieve so-called homogeneous distribution of an interaction (electric field, stress, strain) within the sample. Besides, worked out with a large expenditure of energy and cost, the prism is usually useless in other applications (destructive method). Therefore, an “elder” method of measurement of refractive indices by measuring shift of the refracted beam of light in a plane-parallel plate has been reconsidered in this paper. The sample itself may be a cuboid (if one wishes to measure all of three principal refractive indices in optically biaxial crystal), or just a crystalline boule in which one is cutting off the conical and tail parts and by suitable mechanical treatment (lapping and polishing) reveals a pair of plane parallel surfaces properly oriented to crystallographic (or principal axes of the optical indicatrix) directions. In such case, however, one can only measure one (isotropic crystals) or two (optically uniaxial crystals) refractive indices. However, in case of this method as opposed to the prism method one can repeat the measurement a couple of times, e.g. after a series of consecutive annealing, when this is either impossible or undesirable to cut the boule into smaller pieces prior to the final annealing (nondestructive method). The error depends on the angle of incidence and on sample (boule) thickness and is usually of the order of 0.001. However, in the future it is expected that the error can be reduced by implementing an electronic readout of the beam shift below 1μm. Working of the method has been illustrated with a couple of examples in GdCOB (biaxial), LiNbO3 (uniaxial) and YAG:Cr,Mg (isotropic) crystals.

Reversible conformation-driven order–order transition of peptide-mimic poly(n-alkyl isocyanate) in thin films via selective solvent-annealing

We report for the first time the conformational and structural details of peptide-mimic poly(n-hexyl isocyanate) (PHIC). PHIC is a representative poly(n-alkyl isocyanate)s, which have received significant attention because of their unique stiff chain characteristics and potential applications in various fields. A well-ordered hexagonal close packing structure of PHIC with 83 helical conformation was clearly observed in the nanoscale thin films that were selectively annealed with carbon disulfide (CS2). A well-ordered multi-bilayer structure of the polymer with β-sheet conformation was also clearly formed in the films that were selectively annealed with toluene. In addition, a fully reversible transformation between these two self-assembled structures was demonstrated by consecutive annealings with CS2 and toluene. A family of peptide-mimic polymers — polyisocyanates with linear alkyl side groups — are known to have a stiff helical backbone. These structural features have garnered attention for the development of chiral recognition, optical switches, liquid crystals or degradable materials. Yet the exact conformation the chains adopt, and how they pack in the solid state, remains unclear. Through detailed characterization, Moonhor Ree, Jae-Suk Lee and co-workers in Korea have now confirmed that, in a thin film, the polymer ‘poly(n-hexyl isocyanate)’ forms one of two different, well-ordered structures. The two morphologies were obtained, and reversibly converted into each other, by annealing under different solvent vapours. In the presence of carbon disulfide, helical chains self-assembled into a hexagonal close packing structure, whereas the use of toluene yielded a multi-bilayer lamellar structure consisting of polymer chains in β-sheet conformation. This intriguing transformation arises from the solvent molecules' different affinities with the backbone and side groups of the polymer chain. Peptide-mimic poly(n-hexyl isocyanate) (PHIC) with stiff chain characteristics demonstrated to selectively form a well-ordered hexagonal close packing structure with 83 helical conformation in the nansocale thin films annealed with carbon disulfide. Moreover, this polymer showed to selectively form a well-ordered multi-bilayer structure with β-sheet conformation in the thin films annealed with toluene. These two self-assembled structures were reversibly transformed by consecutive annealing with carbon disulfide and toluene. These chain conformations and self-assembled structures were confirmed by synchrotron grazing incidence X-ray scattering analysis.

Evaluation of recipes for obtaining single terminated perovskite oxide substrates

We have re-assessed different methods to obtain single terminated perovskite oxide substrate surfaces of SrTiO3, LaAlO3 and NdGaO3. The surfaces have been probed by a combination of atomic and lateral force microscopy, X-ray photoelectron spectroscopy and reflection high-energy electron diffraction. (001)SrTiO3 surfaces were prepared with HF or plasma etching and annealing, (001)LaAlO3 surfaces were prepared with or without HCl etching and a consecutive annealing at 750–1100°C, and (110)NdGaO3 surfaces were only annealed. Two of the recipes have previously been suggested to result in A-site terminated surfaces. However, except for the case of high-temperature annealed LaAlO3 where we observe a double-terminated surface, our data suggest that the single terminated surfaces obtained by these methods were of B-site type.

Correlation between residual stress and plastic strain amplitude during low cycle fatigue of mechanically surface treated austenitic stainless steel AISI 304 and ferritic–pearlitic steel SAE 1045

Mechanical surface treatments such as deep rolling are known to affect the near-surface microstructure and induce, e.g. residual stresses and/or increase the surface hardness. It is well known that, e.g. compressive residual stress states usually increase the lifetime under fatigue loading. The stress relaxation behaviour and the stability of the residual stress during fatigue loading depend on the mechanical surface treatment method. In this paper three different surface treatments are used and their effects on the low cycle fatigue behaviour of austenitic stainless steel (AISI 304) and ferritic–pearlitic steel (SAE 1045) are investigated. X-ray diffraction is applied for the non-destructive evaluation of the stress state and the microstructure. It is found that consecutive deep rolling & annealing as well as high temperature deep rolling produce more stable near-surface stress states than conventional deep rolling at room temperature. The plastic strain amplitudes during fatigue loading are measured and it is shown that they correlate well with the induced residual stress and its relaxation, respectively. Furthermore, Coffin–Manson plots are presented which clearly show the correlation between the plastic strain amplitude and the fatigue lifetime.

Electrical and ellipsometry study of sputtered SiO 2 structures with embedded Ge nanocrystals

SiO 2 layer structures with a middle layer containing Ge nanocrystals were prepared by sputtering on n- and p-type Si substrates, and by consecutive annealing. Ge content in the middle layer was varied in the range of 40–100%. Most of the structures exhibited low breakdown voltages. The current through the structures became Schottky-like after breakdown. However, some p-type samples showed a considerable memory effect. It was obtained by spectroscopic ellipsometry that the middle layer contains amorphous Ge phase as well. The results also suggest intermixing of the layers during the sputtering and/or the annealing process.

Epitaxial re-crystallization of the Ni/MgO(0 0 1) interfaces

Metal/ceramic interfaces have become important for advanced technologies in a variety of ways. To effectively tailor their properties, it is important to understand the mechanisms which govern the structural formation of the systems during deposition or post-deposition processing. Here, results on epitaxial re-crystallization of the Ni/MgO(0 0 1) interfaces are reported: (i) as deposited, the Ni films were grown on the MgO(0 0 1) substrates epitaxially, (ii) consecutive thermal annealing incited the process of re-crystallization, which led to the substantial improvement of their crystalline quality. The restructuring proceeded in a non-linear way, indicating that an intricate structural evolution was triggered in the system. Based on the results of the X-ray diffraction and Rutherford backscattering/channeling, the effect of thermal processing on the structural transformation of the Ni/MgO(0 0 1) interface is discussed in this paper.

A use of Ramachandran potentials in protein solution structure determinations.

A strategy is developed to use database-derived phi-psi constraints during simulated annealing procedures for protein solution structure determination in order to improve the Ramachandran plot statistics, while maintaining the agreement with the experimental constraints as the sole criterion for the selection of the family. The procedure, fully automated, consists of two consecutive simulated annealing runs. In the first run, the database-derived phi-psi constraints are enforced for all amino acids (but prolines and glycines). A family of structures is then selected on the ground of the lowest violations of the experimental constraints only, and the phi-psi values for each residue are examined. In the second and final run, the database-derived phi-psi constraints are enforced only for those residues which in the first run have ended in one and the same favored phi-psi region. For residues which are either spread over different favored regions or concentrated in disallowed regions, the constraints are not enforced. The final family is then selected, after the second run, again only based on the agreement with the experimental constraints. This automated approach was implemented in DYANA and was tested on as many as 12 proteins, including some containing paramagnetic metals, whose structures had been previously solved in our laboratory. The quality of the structures, and of Ramachandran plot statistics in particular, was notably improved while preserving the agreement with the experimental constraints.

Exchange biasing of oxidized NiFe 81/19

The influence of breaking the vacuum while depositing an exchange coupled multilayer system for a GMR spin valve sensor was investigated, focusing particularly on the relationship between etching time and exchange coupling properties of the antiferromagnet to the ferromagnet. A Cr/sub 46/Mn/sub 46/Pt/sub 8/ antiferromagnet was used to induce a unidirectional anisotropy in a Ni/sub 81/Fe/sub 19/ ferromagnetic layer. Topically, the exchange coupled 30 nm CrMnPt/12 nm NiFe films exhibited an exchange field of approximately 80 Oe by depositing the layers without breaking the vacuum and no consecutive annealing process. Unloading the NiFe layer and exposing it to the air required a sputter etching process before depositing the antiferromagnet to accomplish exchange coupling. For achieving optimal results, the etching time has to match the time required for removing the oxide film but not for etching the NiFe layer any further. However, layer systems deposited by breaking the vacuum displayed a reduction of the exchange field of roughly 50%.